1. Field of the Invention
The present invention relates to a wireless communication system, and more particularly to a system and method which have applied a mono-pulse scheme to a base station antenna with a circular array structure for estimating the direction of a mobile station.
2. Description of the Related Art
Typically, an antenna facilitates communication by a terminal by implementing conversion between electrical signals expressed by voltage and electric current and electromagnetic signals expressed by electric field and magnetic field. A wireless communication system for performing communication by employing the antenna as described above performs the communication through the air instead of via wire line. In other words, an antenna transmits and receives electromagnetic signals within its special boundaries, and performs an inter-conversion with electrical signals.
A wireless communication system includes a plurality of base stations for providing service to service areas with predetermined sizes, and a plurality of mobile stations for receiving the service from the base station. The wireless communication system exchanges data between the base station and the mobile station by means of the antenna. The base station divides and uses its own service area, i.e. a cell, according to a transitional plan, etc., in order to reduce interference and to delay increasing the base station's service area containing large traffic flow. For example, the base station uses a service area divided into sectors at an angle of 120°, 60° or 45°. Hereinafter, a wireless communication system in which each two of six antennas are assigned to each of three 120° sectors will be described with reference to FIG. 1.
FIG. 1 is a diagram schematically illustrating an antenna structure with three sectors in a base station of a general wireless communication system.
Referring to FIG. 1, the wireless communication system uses six antennas as illustrated in FIG. 1 in order to divide an entire cell into three sectors. That is, the cell of the base station is divided with an angle of 120° so as to generate three sectors, i.e. a first sector 100, a second sector 130 and a third sector 160. Each of the sectors uses two antennas and the antenna is a directional antenna. The first sector 100 includes two directional antennas 101 and 103. The directional antennas 101 and 103 represent antennas designed to have directivity and comprise wireless antennas for forming a beam only in a specific azimuth angle. Typically, the directional antenna has a reflector attached to a rear portion of an isotropic antenna, thereby causing electromagnetic waves to propagate only in a constant direction. The first sector 100 has the same structure as those of the second sector 130 and the third sector 160, and performs the same operation as those of the second sector 130 and the third sector 160. As a result, the antenna system with three sectors divides an entire cell into three sectors, provides separate directional antennas in each sector, and communicates with mobile stations.
However, when the base station antenna as described above is used, it is impossible to estimate or find out the location of a mobile station existing in a cell of the base station.
When a service area changes according to movement of a mobile station, the base station performs handover in order to continuously maintain the current communication channel. If handover is performed between sectors of the same base station, the base station and the mobile station perform the handover while exchanging information between themselves. The base station understands a sector, through which the base station communicates with the mobile station, by means of the inter-sector handover method as described above. Further, when the handover method as described above is used, information is exchanged between the mobile station and the base station. However, much time is required during handover due to the information exchange as described above.
The wireless communication system designs the structure of the base station sector. However, the directivity of the directional antenna in each sector has been fixed according to the initially designed structure of the sector. Therefore, it is impossible to freely adjust the directivity of the antenna. In addition, the base station using the antenna cannot freely adjust beam patterns of the antenna for sectoring.
In each sector of the wireless communication system, two antennas are horizontally installed at a distance greater than several wavelengths apart from each other in order to perform independent reception. Therefore, it is possible to obtain space diversity. However, the base station antenna must have a size designed to accommodate the intervals between the antennas.